The present application relates to an electrode arrangement for high power electric arc furnaces. Such furnaces are employed particularly in the manufacture of steel and are preferably operated with three-phase current.
An electric arc furnace is known to have a nonlinear current/voltage characteristic. With an electrode which is burning steadily and under constant operating conditions, the frontal face under which the arc burns has a distinctly defined outline which remains unchanged even while the electrode burns down. Since the consumption of the frontal face is caused essentially by the fact that the sublimation temperature of graphite is exceeded in the area of the base of the arc, the conclusion can be drawn that every point of the frontal face is under stress, on the average, approximately for the same time. The outline of the frontal face ascends toward the outside with reference; to the center of the furnace, so that the length of the arc is shorter in the center of the furnace than the corresponding length at the outside. Moreover, the equilibrium of the electromagnetic forces attacking the arc causes the arc to slope further toward the outside in the outer positions, i.e. to be additionally extended there.
With current intensities in the order of magnitude of 10.sup.4 A and more, the voltage requirement of an electric arc depends essentially only on the length of the arc. Since the different arc lengths at different times require different arc voltages, maintaining the frontal face contour inevitably leads to irregular amplitude fluctuations in the arc current which, due to corresponding voltage drops in the supplying network, result in voltage fluctuations, also called flicker voltages.
In the desire to increase the power of electric arc furnaces, the arc current, rather than the voltage, is increased in order to obtain a relatively short arc and thus a better power yield. For this purpose, experiments have been made with graphite electrodes which has a diameter up to 70 cm. However, it was found that difficulties arose if the diameters were more than 60 cm.